Make a 2D sprite from an object's shape
In the "Scene" tab go to "Passes" and enable "Object Index". Then select the object you want and go to the "Object" tab. Under "Relations" you will find the "Pass Index". Give it a value, example: 1. 
Then go to the compositor and add an ID mask node and a File output node like this:

Set the ID mask node to whatever your object's index is example: 1.
You will get a Black and white image of the silhouette of the object.
Make sure to have a decent resolution so that your image is not pixelated. 
Hope this is what you were looking for.